Tiles such as natural stone plates and artificial stone plates have been used very often in order to form mainly a floor surface and the like. Large-scale tiles recently have been used so often because of their ornamental features and there are two conventional methods for tile flooring construction: a laid mortar method and a pressure bonding method. The former is a method of applying and laying mortar having a low water content together with cements and the like evenly all over an underlying surface and laying tiles on the laid mortar, and is excellent for laying tiles over a large area. However, a concave-convex shape of the underlying surface tends to reflect on an upper surface on which tiles are laid such that the concave-convex shape is thought to prevent uniform adhesion between the tiles and the underlying surface, and tend to cause defects in workmanship by so-called air pockets. On the other hand, the pressure bonding method is to apply and lay adhesive substance (typically mortar) on the underlying surface and to lay and pressure-bond tiles on the laid adhesive substance. However, the trowel with which the mortar is applied and laid is rather small if compared to the large-scale tile such that a craftsman provides the substance to the underlying surface for several times and forms an even top surface of the substance by sweeping for many times the trowel over a laying surface on which a tile is to be laid, which also requires a very high proficiency. And in the pressure bonding method, the mortar is applied and laid, a tile is laid thereon and then pressed by a hammer or the like, and a settling distance during a period of pressing is considered such that it is generally conducted that a concave-convex shape is formed on the top surface of the laid mortar. For example, in order to lay the tile, the adhesive substance (typically mortar) to bond the tile and the underlying surface over which the tile is laid is applied and laid on the underlying surface, the top surface of the laid adhesive substance (typically mortar) is formed in a ridge-and-groove shape where a concave streak and a convex streak are alternately formed in a series. Various things have been proposed to form the top surface of the adhesive substance in such a ridge-and-groove shape (for example, patent reference 1 and so on).
According to this invention, it is described, “the unit rock slab to be adhered to the upper surface of the mortar is positioned at the even level and an even adhesive surface without including air bubbles or the like in the mortar is formed as the mortar flows smoothly to the valley part without collapse of the mortar when the unit rock slab is placed and pressed such that the adhesive efficiency may be improved,” (paragraphs [0010] in detailed explanation of the invention of Patent Reference 1).